hypotonia

Tonic seizures have their onset in the first month of life.  These become refractory as documented by the EEG which shows severe background slowing, multifocal origins, and hypsarrhythmia.  Psychomotor development is severely delayed and accompanied by profound intellectual disability.  The two reported children were unable to stand and never developed speech.  Feeding difficulties requires tube feeding.  Microcephaly eventually develops along with axial hypotonia and limb ataxia.

Brain MRI was normal at 5 months of age in one individual but at 6 years old showed cerebellar atrophy.  Her younger male sibling at 2 months of age had a normal MRI but cerebellar atrophy was present at 3 years of age.  He died at 3.5 years while his older sib died at age 7 years.

ZTTK syndrome is multisystem malformation and developmental disorder with a heterogeneous clinical presentation.  The facial features might suggest the diagnosis at birth but most of the signs are nonspecific including frontal bossing, underdevelopment of the midface, facial asymmetry, low-set ears, broad and/or depressed nasal bridge, and a short philtrum.  Poor feeding and hypotonia in the neonatal period are usually present and physical growth is subnormal resulting in short stature.

Brain imaging may show abnormal gyral patterns, ventriculomegaly, hypoplasia of the corpus callosum, cerebellar hypoplasia, arachnoid cysts, and loss of periventricular white matter.  About half of patients develop seizures and many have intellectual disabilities.  Spinal anomalies include hemivertebrae with scoliosis and/or kyphosis.  Other skeletal features include joint laxity in some patients and contractures in others.  Arachnodactyly, craniosynostosis, and rib anomalies have been reported.  There may be malformations in the GI, GU, and cardiac systems while immune and coagulation abnormalities have also been reported.

Infants feed poorly which is frequently associated with vomiting, failure to thrive, and growth delay.  They are hypothermic, hypoglycemic, and often jaundiced with signs of liver failure noted between birth and 6 months of age and death by approximately 1 year of age.  Hepatosplenomegaly is present early with abnormal liver enzymes, cholestasis, steatosis, and hepatocellular loss followed by cirrhosis with portal hypertension.  Metabolic acidosis, hyperbilirubinemia, hypoalbuminemia, and hypoglycemia are often present.  Mitochondrial DNA depletion in the liver approaches 84-90%.

All patients have encephalopathic signs with evidence of cerebral atrophy, microcephaly, hypotonia.  Hyperreflexia may be present and some infants have seizures.  Muscle tissue, however, has normal histology and respiratory chain activity.

Progressive microcephaly is often noted.  Truncal hypotonia and scoliosis may be present while muscle tone is increased in the extremities in the presence of diminished deep tendon reflexes in other patients.  Dystonic posturing occurs in some families.  Gingival hyperplasia is a common feature and retrognathia is often present.

Brain imaging reveals progressive cerebellar atrophy and a foreshortened corpus callosum in all families.  Various degrees of cerebral atrophy have been identified while intellectual disability may be marked.  Speech delay is common.

Two families have been reported.  The range of severity in symptoms is wide.  Birth may occur prematurely especially in the presence of polyhydramnios.  Postnatal development can be complicated by seizures, chronic lung disease, developmental regression, and renal disease.  Poor growth secondary to feeding difficulties have been reported.  Death can occur in early childhood.

Dysmorphic features include a short neck, bitemporal narrowing, depressed nasal bridge, and proximal limb shortening.  Osteopenia, flexion contractures, and hip dysplasia may be present.  Dilatation of the renal collecting system with increased echogenicity have been reported.  Creatine kinase and serum alkaline phosphatase may be increased and muscle histology shows small, atrophic fibers with increased fibrosis and considerable variations in fiber size.

The neurologic abnormalities become evident soon after birth.  Hypotonia and decreased reflexes may be present early and often there is little psychomotor development subsequently.  Some patients have no or very little speech and may never sit, stand, or walk.  However, there is considerable variation in the clinical picture and other individuals are able to walk and may live into the third decade.  Brain imaging reveals a variety of abnormalities including cerebellar and cerebral hypoplasia.  Respiratory difficulties and poor feeding are often present.

The facial dysmorphism may include brachycephaly with a broad forehead and narrowing of the temporal regions.  The nose may be small and the mouth appears large in the presence of micrognathia and a thin upper lip.